The 53-year-old singer - who tied the knot with the director in December 2000, divorcing eight years later - admits she began working on the film because she was searching to find what "perfect love" really is and questioning why the romance had left their union.
She said: "I'd been married 10 years when I started writing it. And I was certainly asking a kind of existential question that I think people ask when they've been married that long: What is the perfect love? Because when you start off, everything's great and lovely, and the person you've married is flawless, and you're flawless.
"Then time goes by, and you share a life, you have children, and there are cracks in the veneer. It's not as romantic as it used to be. You think, 'This isn't what I thought it was going to be,' and, 'How much am I willing to sacrifice?' "
Despite their split, Madonna - who had sons Rocco, 11, and adopted David, five, with Guy - insists she is still romantic and believes in "true love".
The 'Hung Up' hitmaker - who is now dating dancer Brahim Zaibat - told the new issue of Newsweek magazine: "When you get to the end of the movie, I think it's very clear they really loved each other, and that I am a romantic and that I do believe in true love."